Deconvolution from wave-front sensing (DWFS) has been proposed as a method for achieving high-resolution images of astronomical objects from ground-based telescopes. The technique consists of the simultaneous measurement of a short-exposure focal-plane speckled image, as well as the wave front, by use of a Shack-Hartmann sensor placed at the pupil plane. In early studies it was suspected that some problems would occur in poor seeing conditions; however, it was usually assumed that the technique would work well as long as the wave-front sensor subaperture spacing was less than r(0) (L/r(0) < 1). Atmosphere-induced phase errors in the pupil of a telescope imaging system produce both phase errors and magnitude errors in the effective short-exposure optical transfer function (OTF) of the system. Recently it has been shown that the commonly used estimator for this technique produces biased estimates of the magnitude errors. The significance of this bias problem is that one cannot properly estimate or correct for the frame-to-frame fluctuations in the magnitude of the OTF but can do so only for fluctuations in the phase. An auxiliary estimate must also be used to correct for the mean value of the magnitude error. The inability to compensate for the magnitude fluctuations results in a signal-to-noise ratio (SNR) that is less favorable for the technique than was previously thought. In some situations simpler techniques, such as the Knox-Thompson and bispectrum methods, which require only speckle gram data from the focal plane of the imaging system, can produce better results. We present experimental measurements based on observations of bright stars and the Jovian moon Ganymede that confirm previous theoretical predictions.
[1]
O. Lühe.
Signal transfer function of the Knox–Thompson speckle imaging technique
,
1988
.
[2]
M C Roggemann,et al.
Biased estimators and object-spectrum estimation in the method of deconvolution from wave-front sensing.
,
1994,
Applied optics.
[3]
D G Voelz,et al.
First astronomical application of postdetection turbulence compensation: images of alpha Aurigae, nu Ursae Majoris, and alpha Geminorum using self-referenced speckle holography.
,
1990,
Applied optics.
[4]
Jérôme Primot,et al.
Deconvolution from wave-front sensing: a new technique for compensating turbulence-degraded images
,
1990
.
[5]
C. Papaliolios,et al.
Effects of photon noise on speckle image reconstruction with the Knox-Thompson algorithm. [in astronomy]
,
1983
.
[6]
K. Knox,et al.
Recovery of Images from Atmospherically Degraded Short-Exposure Photographs
,
1974
.
[7]
M C Roggemann,et al.
Signal-to-noise ratio for astronomical imaging by deconvolution from wave-front sensing.
,
1994,
Applied optics.
[8]
B M Welsh,et al.
Performance analysis of the self-referenced speckle-holography image-reconstruction technique.
,
1993,
Applied optics.